Answer:
What does everyone know how to open but not how to close?
What is lengthened by being cut at both ends?
We are all around, yet to us you are half blind. Sunlight makes us invisible, and difficult to find
A man calls his dog from the opposite side of the river. The dog crosses the river without getting wet, and without using a bridge or boat. How?
What kind of nut is empty at the center and has no shell.
As round as an apple. As deep as a cup. All the king's horses can't pull it up.